The present invention generally relates to catalyst supports, catalyst composites containing the catalyst supports, and methods of making and employing the catalyst supports and catalyst composites. The present invention particularly relates to catalyst materials and methods associated with the purification of terephthalic acid.
Catalytic processes are indispensable in the chemical industry. Frequently, catalytic processes employ a catalyst that is incorporated on a support. Effective use of the catalyst often corresponds to the quality of the catalyst support. Poor quality catalyst supports, due to at least one of physical degradation, chemical degradation, undesirable properties, and inconsistent properties, limit the effectiveness of catalysts incorporated therein. Conditions such as high temperatures, high pressures, and high or low pH present challenges to the integrity of catalyst supports.
For example, conventional catalyst composites for the purification of terephthalic acid by the Amoco mid-continent process (PTA catalysts) are composed of palladium supported on granular 4xc3x978 mesh carbon. These catalyst composites are designed to remove the two major impurities present in crude terephthalic acid: namely, yellow color and 4-carboxy benzaldehyde.
Carbon is the preferred support material for conventional PTA catalysts because it is essentially the only readily available material that can simultaneously yield an effective catalyst for color removal, 4-carboxy benzaldehyde removal, and also withstand the extremely corrosive environment of the terephthalic acid purification process. Although conventional carbon supported PTA catalysts have been used extensively over the past 20 years, such catalyst composites suffer from several well known disadvantages. These disadvantages include: highly irregular shapes leading to possible maldistribution of liquid or gas flows in a catalytic reactor bed utilizing such catalyst composites; shapes having sharp and fragile edges and corners, which tend to break off and contaminate the PTA product with undesirable dust and black particles; brittleness, which also leads to breakage and dust/black particles contaminating the PTA product; natural origin,i.e., coconut shell, which leads to nonuniformity from one growing season to another and consequent inconsistency of the carbon support; and being commonly derived from nutshells, such activated carbon has very small pores, leading to the requirement of locating all of the active catalytic metal near the external surface of the particles, where the metal is undesirably susceptible to loss during movement and abrasion that occurs during shipping and handling.
Non-carbon catalyst supports have been employed in catalytic processes in attempts to overcome the disadvantages associated with conventional carbon supported catalysts. Non-carbon catalyst supports include alumina supports, silica supports, alumina-silica supports, various clay supports, titania, and zirconium supports. However, there are at least one of several disadvantages associated with non-carbon catalyst supports: namely, that they may loose physical strength, that they are dissolved in corrosive environments (such as hot aqueous solutions of terephthalic acid) and that catalysts made using such supports have difficulties in removing undesirable color from crude terephthalic acid.
Improved catalyst supports and catalyst composites are therefore desired. Specifically, improved PTA catalyst supports and PTA catalyst composites are desired to provide improved methods of purifying terephthalic acid.
The following presents a simplified summary of the invention in order to provide a basic understanding of some of its aspects. This summary is not an extensive overview of the invention and is intended neither to identify key or critical elements of the invention nor to delineate its scope. The sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention is designed to address at least one of and preferably all of the above described disadvantages by providing a carbon-containing catalyst support that includes at least a carbonaceous material and a polymer. The components are mixed and the polymer sintered or thermoset to provide a non-crushable, non-friable, and non-breakable composite. A catalytically active metal can be supported on the carbonaceous material prior to mixing, or on the composite after mixing and heating the mixture to sinter or thermoset the polymer.
In one embodiment, the present invention relates to a catalyst support including a formed mixture of at least about 5% by weight of an activated carbonaceous material and at least about 5% by weight of a polymer sintered or thermoset after mixing with the carbonaceous material.
In another embodiment, the present invention relates to a catalyst composite including a catalyst support having at least about 5% by weight of an activated carbonaceous material and at least about 5% by weight of a sinterable or thermosetting polymer, and at least about 0.05% by weight of a catalytically active metal supported on the catalyst support.
In yet another embodiment, the present invention relates to a method of making a catalyst composite that includes mixing a carbonaceous material with a sinterable or thermosetting polymer to obtain a mixture, heating the mixture to sinter or thermoset the polymer and obtain a catalyst support, and supporting a catalytically active metal on the catalyst support to obtain a catalyst composite.
In a further embodiment, the present invention relates to a method of making a catalyst composite that includes supporting a catalytically active metal on a carbonaceous material, mixing the carbonaceous material, having the catalytically active metal supported thereon, with a sinterable or thermosetting polymer to form a mixture, and heating the mixture to sinter or thermoset the polymer.
Other advantages and novel features of the invention will become apparent from the following detailed description of the invention. The detailed description provides certain illustrative examples of the invention. These examples are indicative of but a few of the various ways in which the principles of the invention can be employed.